I don't know anything about "buddyboxing" but my preference would be to have her controlling her plane with her Tx (HK T4a). If I see her getting in to trouble I let go of my trainer switch and have control. The reason for this setup would be a panicing GF forgetting to release the switch (I know her to well ). It doesn't matter witch Tx is bound to the Rx because they both can bind to the same Rx's.

So in a nutshell:GF flying with HK T4aMe holding 9x trainer-switch and taking over if nessesaryReceiver doesn't matter

I haven't tried it myself, but reports are that it is quite effective.You will need male to male reciever patch cords to make your connections, and if there's not much room in the radio compartment of the plane it could be a problem. FWIW

In short this system uses the master tx to send control signals to rx. Student tx does not transmit but sends signals to teacher tx for transmission. Teacher tx decides what to do with signals depending on setup (trainer switch etc). As far as who controls what, technically it is going to be easier for the 9x to be the tx to the aircraft and passing through the student control signals. I cannot see a trainer switch on the HK unit so using that is out of the question.

Jim's suggestion is another good idea, but does require the aircraft to have receivers from both tx units installed. So you will need room in the aircraft to fit it.

This is 4 channel version. Check the files section for how to wire it in.

If you are going to go down the traditional buddy box system, your next issue is going to be creating a cable with a s-video (not ps2 as I originally said) style connector at one end and a mono 3.5mm at the other. From what I can work out pin 1 goes to centre and the shell/ground goes to ground.

Otherwise pickup one of the suggested aircraft based units and install that with the two rx. Setup the 5th channel on the 9x to be controlled from the trainer switch, test and double check all works correctly, and off you go.

Frazzy wrote:I thought the trainer had control over the panic switch...

To reiterate: As I understand it (and this is how I set it up) the preferred method of a buddy box setup is that the trainer tx is set-up so the trainer pulls and HOLDS the trainer switch to relinquish control TO the student tx. Releasing the switch reverts control back to the trainer tx.

So the trainer has to actively hand control over to the student and continues to hold the trainer switch until such time that they need to regain control.

The trainer switch is usually a momentary switch i.e. the switch is spring loaded so it always returns to the same position, unlike an on/off switch.